The present invention relates to a plurality of dispersed power sources linked to a high-voltage-to-low-voltage transformer of a commercial power system, and in particular, to an output suppressing method of a plurality of dispersed power sources and a dispersed power source managing system.
For example, solar batteries and the like are independent DC (Direct Current) power sources capable of outputting a DC power without interposition of other energy sources and known as clean simple energy sources that discharge no toxic substance.
FIG. 3 shows a conventional power supply system that transforms a DC power generated by such an independent DC power source into an AC (Alternating Current) power and supplies the resulting power to a general AC load or an existing commercial power system.
In the power supply system shown in FIG. 3, a plurality of dispersed power sources 101a, 101b, 101c, 101d and 101e are connected to a high-voltage 6600-V system wire to low-voltage 200-V system wire transformer 106 (hereinafter referred to as a transformer) of a commercial power system 102. Among these plurality of dispersed power sources 101a, 101b, 10c, 101d and 101e, the dispersed power sources 101a, 101b, 101c and 101d have same construction. The dispersed power source 101a is constructed of a solar battery 103 that serves as a DC power source, a power conditioner 104 for transforming the DC power into an AC power, an electrical load 105 connected to the output side of this power conditioner 104, and a breaker 107 that connects or disconnects the power conditioner 104 to or from the commercial power system 102 and is linked to the commercial power system 102. The dispersed power source 101a executes maximum power point tracking control for producing a maximum output of the solar battery 103 in the daytime during which there is light of solar radiation. Then, the dispersed power source 101a transforms the obtained DC power into an AC power by the power conditioner 104, supplies the obtained AC power to the electrical load 105, supplies the AC power to the commercial power system 102 when a surplus power is generated (this is called a reverse power flow phenomenon) and supplies the AC power from the commercial power system 102 to the electrical load 105 when power shortage occurs.
When the dispersed power source 101a supplies the surplus power to the commercial power system 102, a voltage at a power receiving point RPa of the dispersed power source 101a increases in comparison with the case where no surplus power is supplied. That is, since a current reversely flows from the dispersed power source 101a to the commercial power system 102, a voltage increase value ΔV at the power receiving point RPa is determined by the internal impedance of the transformer 106, the impedance of a wiring 112a extended from the power receiving point RPa to the transformer 106 and the reversely flowing generated current. According to the Electricity Enterprises Act, the voltage at the power receiving point RPa of the dispersed power source 101a is required to be maintained within a proper value range of 101±6 V with respect to the standard voltage of 100 V. If the voltage at the power receiving point RPa increases and exceeds an upper limit of a proper value as a consequence of the supplying of the surplus power from the dispersed power source 101a to the commercial power system 102, then the output of the power conditioner 104 is suppressed so as not to exceed the upper limit of the proper value. In concrete, if the voltage at the power receiving point RPa of the dispersed power source 101a exceeds the upper limit of the proper value, then the power conditioner 104 executes the control of suppressing the output power by limiting the amount of the DC power from the solar battery 103 with the normally executed maximum power point tracking control stopped. By thus suppressing the output power of the power conditioner 104, the increase in the voltage at the power receiving point RPa of the dispersed power source 101a is suppressed by reducing the current reversely flowing from the dispersed power source 101a to the commercial power system 102. If the voltage at the power receiving point RPa of the dispersed power source 101a falls below the upper limit of the proper value, then the power conditioner 104 cancels the output suppressing control and restarts the maximum power point tracking control. By repetitively executing these control sequences, the voltage at the power receiving point RPa of the dispersed power source 101a is maintained at the proper value.
Moreover, among the plurality of dispersed power sources 101a, 101b, 101c, 101d and 101e, the dispersed power source 101e differs from the dispersed power sources 101a, 101b, 101c and 101d only in that it has a storage battery 108. That is, the dispersed power source 101e is constructed of a solar battery 103 that serves as a DC power source, a storage battery 108, a power conditioner 104 for transforming the DC power into an AC power, an electrical load 105 connected to the output side of this power conditioner 104, and a breaker 107 that connects or disconnects the power conditioner 104 to or from the commercial power system 102 and is linked to the commercial power system 102. The dispersed power source 101e transforms a DC power obtained by executing the maximum power point tracking control for producing the maximum output of the solar battery 103 in the daytime during which there is light of solar radiation into an AC power by the power conditioner 104, supplies the obtained AC power to the electrical load 105. When power shortage occurs, the AC power of the shortage is supplied from the commercial power system 102 to the electrical load 105. When a surplus power occurs, the power is not supplied to the commercial power system 102 but stored into the storage battery 108 located on the input side of the power conditioner 104. As described above, the voltage at the power receiving point RPe of this dispersed power source 101e does not increase unless the reverse flow occurs from the dispersed power source 101e to the commercial power system 102, and the voltage at the power receiving point RPe of this dispersed power source 101e can maintain the proper value.
However, the plurality of conventional dispersed power sources 101a, 101b, 10c, 101d and 101e individually execute the output suppression control. Therefore, the outputs are controlled sequentially from the dispersed power source of which the voltage at the power receiving point exceeding the upper limit of the proper value is detected earliest among the plurality of dispersed power sources 101a, 101b, 10c, 101d and 101e. Then, the voltages at the power receiving points of all the dispersed power sources 101a, 101b, 10c, 101d and 101e enter a state in which they do not exceed the upper limit of the proper value. In the above state, there exist in mixture the dispersed power source of which the output suppression is being executed and the dispersed power source of which the output suppression is not being executed. Accordingly, there has been a problem that the dispersed power source of which the output suppression is being executed is partially handled in view of the effective use of the power from the solar battery in comparison with the dispersed power source of which the output suppression is not required to be executed.
Moreover, when the storage battery 108 is provided inside the dispersed power source 101e and the surplus power is stored in the storage battery 108 without making a reverse flow to the commercial power system 102, the voltage at the power receiving point RPe of the dispersed power source 101e can be maintained low. However, for the above purpose, there has been a problem that the capacity of the storage battery 108 has been required to be increased, leading to the cost increase of the dispersed power source 101e. 